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# What Is a Synchronous Circuit?

Article Details
• Written By: M. McGee
• Edited By: Lauren Fritsky
2003-2020
Conjecture Corporation
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A synchronous circuit is a type of digital circuit that has its timings determined by an external clock signal. These circuits are designed to operate at precise times or in precise circumstances. Essentially, whenever the situation is correct, the system clock will send a signal to the circuit to activate. It will do whatever it is designed to do and then turn off until it gets another signal. These systems are built to operate with split-second timing, but there is commonly a delay between the clock and the synchronous circuit as the signal travels through the system.

In order to understand exactly how a synchronous circuit operates, it is necessary to know how the systems they are used in work. First, a synchronous circuit is part of a digital system. This means that the signals it receives operate in two functions: on or off. These systems are a common part of modern technology, particularly in computers and computer-controlled devices.

The largest portion of the external operation of a synchronous circuit is the clock. This is a common part of more complex digital systems and it is used to keep track of timings. Unlike traditional clocks, these timings aren’t typically based on actual time; they are based on operational states. Basically, this is the part of the digital system that makes sure everything happens when it is supposed to.

When a specific operational state occurs, the clock will send a signal to the synchronous circuit. This will turn on the circuit’s function and it will operate as designed. This could be as simple as letting a signal or electrical power pass through it for a few milliseconds, or it could be a first step in a large multistage digital function. Whatever the circuit’s purpose, it will do it one time and then turn off. It will turn back on only after getting another signal.

Since these circuits are tied so closely to the system clock, they are typically used to perform activities that need to happen at precise times. While this may seem like a highly important concept, the majority of common digital systems rely on close timing to keep the entire system operating correctly. Many of these timings are heavy on software control; hardwired control, like in a synchronous circuit, is less common.

The true use of a hardware system is in the number of actions that need to happen in order for it to operate. When software timing activates, the processing of the command is based on the other things happening on the system. If the processor is busy, the delay could throw off the timings. Hardware systems don’t have those extra steps; a synchronous circuit can be connected directly to the clock.